Network Working Group D. Crocker
Internet-Draft Brandenburg Consulting
Expires: May 2, 2001 A. Diacakis
F. Mazzoldi
Network Projects Inc.
C. Huitema
Microsoft Corporation
G. Klyne
Content Technologies
M. Rose
Invisible Worlds
J. Rosenberg
R. Sparks
dynamicsoft
H. Sugano
Fujitsu Laboratories Ltd.
November 2000
A Common Profile for Instant Messaging (CPIM)
draft-ietf-impp-cpim-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on May 2, 2001.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
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Semantics and data formats for common services of Instant Messaging
and online Presence, independent of underlying transport
infrastructure, are described. The CPIM profile meets the
requirements specified in RFC 2779 using a minimalist approach
allowing interoperation of a wide range of IM and Presence systems.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 A Note on The Examples . . . . . . . . . . . . . . . . . . 4
2. Abstract Messaging Service . . . . . . . . . . . . . . . . 5
2.1 Overview of the Messaging Service . . . . . . . . . . . . 5
2.2 Identification of INSTANT INBOXes . . . . . . . . . . . . 6
2.2.1 Address Resolution . . . . . . . . . . . . . . . . . . . . 6
2.2.1.1 Domain Name Lookup . . . . . . . . . . . . . . . . . . . . 6
2.2.1.2 Processing SRV RRs . . . . . . . . . . . . . . . . . . . . 7
2.2.1.3 Processing Multiple Addresses . . . . . . . . . . . . . . 7
2.3 Format of Instant Messages . . . . . . . . . . . . . . . . 8
2.4 The Messaging Service . . . . . . . . . . . . . . . . . . 9
2.4.1 The Message Operation . . . . . . . . . . . . . . . . . . 9
2.4.2 Looping . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. Abstract Presence Service . . . . . . . . . . . . . . . . 11
3.1 Overview of the Presence Service . . . . . . . . . . . . . 11
3.2 Identification of PRESENTITIES . . . . . . . . . . . . . . 14
3.3 Format of Presence Information . . . . . . . . . . . . . . 15
3.4 The Presence Service . . . . . . . . . . . . . . . . . . . 16
3.4.1 The Subscribe Operation . . . . . . . . . . . . . . . . . 16
3.4.2 The Notify Operation . . . . . . . . . . . . . . . . . . . 18
3.4.3 The Unsubscribe Operation . . . . . . . . . . . . . . . . 19
4. Security Considerations . . . . . . . . . . . . . . . . . 20
4.1 Threats . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 Hop-by-hop security . . . . . . . . . . . . . . . . . . . 21
4.3 End-to-end security . . . . . . . . . . . . . . . . . . . 22
4.3.1 Instant messages . . . . . . . . . . . . . . . . . . . . . 22
4.3.2 Presence service . . . . . . . . . . . . . . . . . . . . . 22
5. IANA Considerations . . . . . . . . . . . . . . . . . . . 23
5.1 The IM URI Scheme . . . . . . . . . . . . . . . . . . . . 23
5.2 The PRES URI Scheme . . . . . . . . . . . . . . . . . . . 23
6. The Common Service DTD . . . . . . . . . . . . . . . . . . 24
7. The Messaging Service DTD . . . . . . . . . . . . . . . . 25
8. The Presence Service DTD . . . . . . . . . . . . . . . . . 26
9. The Presence Information DTD . . . . . . . . . . . . . . . 28
References . . . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . 29
A. IM URL IANA Registration Template . . . . . . . . . . . . 32
A.1 URL scheme name . . . . . . . . . . . . . . . . . . . . . 32
A.2 URL scheme syntax . . . . . . . . . . . . . . . . . . . . 32
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A.3 Character encoding considerations . . . . . . . . . . . . 32
A.4 Intended usage . . . . . . . . . . . . . . . . . . . . . . 32
A.5 Applications and/or protocols which use this URL scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
A.6 Interoperability considerations . . . . . . . . . . . . . 32
A.7 Security considerations . . . . . . . . . . . . . . . . . 33
A.8 Relevant publications . . . . . . . . . . . . . . . . . . 33
A.9 Person & email address to contact for further information 33
A.10 Author/Change controller . . . . . . . . . . . . . . . . . 33
A.11 Applications and/or protocols which use this URL scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
B. PRES URL IANA Registration Template . . . . . . . . . . . 34
B.1 URL scheme name . . . . . . . . . . . . . . . . . . . . . 34
B.2 URL scheme syntax . . . . . . . . . . . . . . . . . . . . 34
B.3 Character encoding considerations . . . . . . . . . . . . 34
B.4 Intended usage . . . . . . . . . . . . . . . . . . . . . . 34
B.5 Applications and/or protocols which use this URL scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
B.6 Interoperability considerations . . . . . . . . . . . . . 34
B.7 Security considerations . . . . . . . . . . . . . . . . . 35
B.8 Relevant publications . . . . . . . . . . . . . . . . . . 35
B.9 Person & email address to contact for further information 35
B.10 Author/Change controller . . . . . . . . . . . . . . . . . 35
B.11 Applications and/or protocols which use this URL scheme
name . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
C. Issues of Interest . . . . . . . . . . . . . . . . . . . . 36
C.1 Address Mapping . . . . . . . . . . . . . . . . . . . . . 36
C.1.1 Source-Route Mapping . . . . . . . . . . . . . . . . . . . 36
Full Copyright Statement . . . . . . . . . . . . . . . . . 37
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1. Introduction
To achieve interoperation of IM systems that are compliant with RFC
2779[8], there must be a common agreement on both Instant Messaging
and Presence services. This memo defines such an agreement according
to the philosophy that there must be no loss of information between
IM systems that are minimally conformant to RFC2779.
This memo focuses on interoperation. Accordingly only those aspects
of IM that require interoperation are discussed. For example, the
"open instant inbox" operation is not applicable as this operation
occurs within a single IM system and not across systems.
Service behavior is described abstractly in terms of operations
invoked between the consumer and provider of a service. Accordingly,
each IM service must specify how this behavior is mapped onto its own
protocol interactions. The choice of strategy is a local matter,
providing that there is a clear relation between the abstract
behavior of the service (as specified in this memo) and how it is
faithfully realized by a particular IM service.
The parameters for each operation are defined using an abstract
syntax. Although the syntax specifies the range of possible data
values, each IM service must specify how well-formed instances of the
abstract representation are encoded as a concrete series of bits.
For example, one strategy might transmit presence information as
key/value pairs, another might use a compact binary representation,
and a third might use nested containers. The choice of strategy is a
local matter, providing that there is a clear relation between the
abstract syntax (as specified in this memo) and how it is faithfully
encoded by an particular IM service.
1.1 Terminology
This memos makes use of the vocabulary defined in RFC 2778[7]. Terms
such as as CLOSED, INSTANT INBOX, INSTANT MESSAGE, OPEN, PRESENCE
SERVICE, PRESENTITY, SUBSCRIPTION, and WATCHER are used in the same
meaning as defined therein.
1.2 A Note on The Examples
In the examples which follow, this memo uses time-sequence diagrams
annotated with XML fragments to illustrate operations and their
parameters. The use of XML is an artifact of this memo's presentation
style and does not imply any requirement for the use of XML in an IM
system.
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2. Abstract Messaging Service
2.1 Overview of the Messaging Service
When an application wants to send a message to an INSTANT INBOX, it
invokes the message operation, e.g.,
+-------+ +-------+
| | | |
| appl. | -- message ------> | IM |
| | | svc. |
+-------+ +-------+
<message source='im:fred@example.com'
destination='im:barney@example.com'
transID='1' />
...
Content-Type: text/plain; charset="us-ascii"
Yabba, dabba, doo!
The service immediately responds by invoking the response operation
containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | | |
| appl. | <----- response -- | IM |
| | | svc. |
+-------+ +-------+
<response status='success' transID='1' />
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2.2 Identification of INSTANT INBOXes
An INSTANT INBOX is specified using the IM URI (Section 5.1)f RFC
822[1] (i.e., "local@domain") is used, where the local-part MUST be
interpreted and assigned semantics only by the system specified in
the domain part of the identifier. Representation of non-ASCII
character sets in local-part strings is limited to the standard
methods provided as extensions to RFC 822[1]
2.2.1 Address Resolution
A client determines the address of an appropriate system running a
server by resolving the destination domain name that is part of the
identifier to either an intermediate relay system or a final target
system.
Only resolvable, fully-qualified, domain names (FQDNs) are permitted
when domain names are used in the messaging service (i.e., domain
names that can be resolved to SRV[9] or A RRs).
2.2.1.1 Domain Name Lookup
A client lexically identifies a domain to which instant messages will
be delivered for processing, a DNS lookup MUST be performed to
resolve the domain[2]. The names MUST be fully-qualified domain names
(FQDNs) Ãù mechanisms for inferring FQDNs from partial names or local
aliases are a local matter.
The lookup first attempts to locate SRV RRs associated with the
domain. If a CNAME RR is found instead, the resulting domain is
processed as if it were the initial domain.
If one or more SRV RRs are found for a given domain, a sender MUST
NOT utilize any A RRs associated with that domain unless they are
located using the SRV RRs; otherwise, if no SRV RRs are found, but an
A RR is found, then the A RR is treated as if it was associated with
an implicit SRV RR, with a preference of 0, pointing to that host.
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2.2.1.2 Processing SRV RRs
To process an IM URI, a lookup is performed for SRVs for the target
domain and a desired IM transport protocol.
For example, if the destination INSTANT INBOX is
"im:fred@example.com", and the sender wishes to use an IM transport
protocol called "SIP", then a SRV lookup is performed for:
_im._sip.example.com.
The returned RRs, if any, specify the next-hop server.
The choice of IM transport protocol is a local configuration option
for each system.
Using this mechanism, seamless routing of IM traffic is possible,
regardless of whether a gateway is necessary for interoperation. To
achieve this transparency, a seperate RR for a gateway must be
present for each transport protocol and domain pair that it serves.
2.2.1.3 Processing Multiple Addresses
When the lookup succeeds, the mapping can result in a list of
alternative delivery addresses rather than a single address, because
of multiple SRV records, multihoming, or both. For reliable
operations, the client MUST be able to try each of the relevant
addresses in this list in order, until a delivery attempt succeeds.
However, there MAY also be a configurable limit on the number of
alternate addresses that can be tried. In any case, the client SHOULD
try at least two addresses. Two types of information are used to rank
the host addresses: multiple SRV records, and multihomed hosts.
Multiple SRV records contain a preference indication that MUST be
used in sorting. Lower numbers are preferrable to higher ones. If
there are multiple destinations with the same preference, and there
is no clear reason to favor one (e.g., by recognition of an easily-
reached address), then the sender MUST randomize them to spread the
load across multiple servers for a specific destination.
The destination host (perhaps taken from the preferred SRV record)
may be multihomed, in which case the resolver will return a list of
alternative IP addresses. It is the responsibility of the resolver to
have ordered this list by decreasing preference if necessary, and the
sender MUST try them in the order presented.
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2.3 Format of Instant Messages
An INSTANT MESSAGE comprises a MIME Multipart/Related,
Type=message/RFC822+XML object, as defined in XML/MIME[5].
Representation of non-ASCII character sets in MIME is a standard
feature of MIME.
Note that the IETF provides numerous technologies that allow end-
users to exchange authenticated and private messages formatted as
MIME objects, c.f., PGP-MIME[4] and S/MIME[6].
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2.4 The Messaging Service
Section 6 and Section 7 define the abstract syntax of the operations
invoked with the service.
Note that the transaction-identifier parameters used with the service
are potentially long-lived. Accordingly, the values of transaction-
identifiers should appear to be unpredictable.
2.4.1 The Message Operation
When an application wants to send an INSTANT MESSAGE, it invokes the
message operation.
The message operation has these parameters:
o the source parameter specifies the INSTANT INBOX on whose behalf
this message is sent (using an IM URI);
o the destination parameter specifies the INSTANT INBOX that the
message should be delivered to (using an IM URI);
o the transID parameter specifies the transaction-identifier
associated with this operation; and,
o the message to be sent.
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When the service is informed of the message operation, it performs
these steps:
1. If the source or destination does not refer to a valid INSTANT
INBOX, a response operation having status "failure" is invoked.
2. If access control does not permit the application to request this
operation, a response operation having status "failure" is
invoked.
3. Otherwise:
1. If the service is able to successfully deliver the message, a
response operation having status "success" is invoked.
2. If the service is unable to successfully deliver the message,
a response operation having status "failure" is invoked.
3. If the service must delegate responsibility for delivery, and
if the delegation will not result in a future authoritative
indication to the service, a response operation having status
"indeterminant" is invoked.
4. If the service must delegate responsibility for delivery, and
if the delegation will result in a future authoritative
indication to the service, then a response operation is
invoked immediately after the indication is received.
When the service invokes the response operation, the transID
parameter is identical to the value found in the message operation
invoked by the application.
2.4.2 Looping
The dynamic routing of instant messages can result in looping of a
message through a relay. Detection of loops is not always obvious,
since aliasing and group list expansions can legitimately cause a
message to pass through a relay more than one time.
[[[ In Internet Mail, counting the number of Received headers is the
accepted technique for guessing that looping is occurring. Use of
this technique will require Instant Messaging to support Received
headers. /editor ]]]
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3. Abstract Presence Service
3.1 Overview of the Presence Service
When an application wants to (periodically) receive the presence
information associated with a PRESENTITY, it invokes the subscribe
operation, e.g.,
+-------+ +-------+
| | | |
| appl. | -- subscribe ----> | pres. |
| | | svc. |
+-------+ +-------+
<subscribe watcher='pres:wilma@example.com'
target='pres:fred@example.com'
duration='86400' transID='2' />
The service immediately responds by invoking the response operation
containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | | |
| appl. | <----- response -- | pres. |
| | | svc. |
+-------+ +-------+
<response status='success' transID='2' duration='3600' />
A WATCHER may have at most one subscription for a PRESENTITY.
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If the response operation indicates success, the service immediate
invokes the notify operation to communicate the presence information
to the WATCHER, e.g.,
+-------+ +-------+
| | | |
| appl. | <------- notify -- | pres. |
| | | svc. |
+-------+ +-------+
<notify watcher='pres:wilma@example.com'
target='pres:fred@example.com'
transID='1234'>
<presence entityInfo='http://www.example.com/fred/'>
<tuple destination='im:fred@example.com'
status='open' />
</presence>
</notify>
If the duration parameter is non-zero, then for up to the specified
duration, the service invokes the notify operation whenever there are
any changes to the PRESENTITY's presence information. Otherwise,
exactly one notify operation is invoked, achieving a one time poll of
the presence information. Regardless, there is no application
response to the notify operation (i.e., the application does not
invoke a response operation when a notify operation occurs).
The application may prematurely cancel a subscription by invoking the
unsubscribe operation, e.g.,
+-------+ +-------+
| | | |
| appl. | -- unsubscribe --> | pres. |
| | | svc. |
+-------+ +-------+
<unsubscribe watcher='pres:wilma@example.com'
target='pres:fred@example.com'
transID='3' />
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The service immediately responds by invoking the response operation
containing the same transaction-identifier, e.g.,
+-------+ +-------+
| | | |
| appl. | <----- response -- | pres. |
| | | svc. |
+-------+ +-------+
<response status='success' transID='3' />
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3.2 Identification of PRESENTITIES
A PRESENTITY is specified using the PRES URI (Section 5.2) scheme.
Briefly, the "addr-spec" syntax of RFC 822[1] (i.e., "local@domain")
is used, where the local-part MUST be interpreted and assigned
semantics only by the host specified in the domain part of the
identifier. Representation of non-ASCII character sets in local-part
strings is limited to the standard methods provided as extensions to
RFC 822[1]
To resolve identifiers associated with the Presence service, the
mechanism defined in Section 2.2.1 is used, except that the
processing of a PRES URI is performed by looking up SRV RRs for a
desired presence transport protocol.
For example, if the destination PRESENTITY is
"pres:fred@example.com", and the sender wishes to use a presence
transport protocol called "PEPP", then a SRV lookup is performed for:
_pres._pepp.example.com.
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3.3 Format of Presence Information
Section 9 defines the syntax for presence information using an XML
DTD.
Each PRESENTITY's presence information contains an "entityInfo"
attribute, and contains one or more "tuple" elements:
o the "entityInfo" attribute specifies arbitrary information about
the PRESENTITY (using a URI); and,
o each "tuple" element specifies information associated with the
PRESENTITY.
Each "tuple" element has a "destination" attribute, a "status"
attribute, and contains arbitrary content:
o the "destination" attribute specifies a URI;
o the "status" attribute is either OPEN or CLOSED; and,
o the content of the "tuple" element contains arbitrary information
about the tuple.
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3.4 The Presence Service
Section 6 and Section 8 define the abstract syntax of the operations
invoked with the service.
An implementation of the service must maintain information about both
presence information and in-progress operations in persistent
storage.
Note that the transaction-identifier parameter used with the service
is potentially long-lived. Accordingly, the values generated for this
parameter should appear to be unpredictable.
3.4.1 The Subscribe Operation
When an application wants to (periodically) receive the presence
information associated with an PRESENTITY, it invokes the subscribe
operation.
The subscribe operation has these parameters:
o the watcher parameter specifies the WATCHER associated with the
subscription;
o the target parameter specifies the PRESENTITY associated with the
presence information;
o the duration parameter specifies the maximum number of seconds
that the SUBSCRIPTION should be active; and,
o the transID parameter specifies the transaction-identifier
associated with this operation.
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When the service is informed of the subscribe operation, it performs
these steps:
1. If the watcher or target parameter does not refer to a valid
PRESENTITY, a response operation having status "failure" is
invoked.
2. If access control does not permit the application to request this
operation, a response operation having status "failure" is
invoked.
3. If the duration parameter is non-zero, and if the watcher and
target parameters refer to an in-progress subscribe operation for
the application, a response operation having status "failure" is
invoked.
4. Otherwise:
1. A response operation having status "success" is immediately
invoked. (If the service chooses a different duration for the
subscription then it conveys this information in the response
operation.)
2. A notify operation, corresponding to the target's presence
information, is immediately invoked for the watcher.
3. For up to the amount of time indicated by the duration
parameter, if the target's presence information changes, and
if access control allows, a notify operation is invoked for
the watcher.
Note that if the duration parameter is zero-valued, then the
subscribe operation is making a one-time poll of the presence
information. Accordingly, Step 4.3 above does not occur.
When the service invokes a response operation as a result of this
processing, the transID parameter is identical to the value found in
the subscribe operation invoked by the application.
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3.4.2 The Notify Operation
The service invokes the notify operation whenever the presence
information associated with a PRESENTITY changes and there are
subscribers to that information.
The notify operation has these parameters:
o the watcher parameter specifies the WATCHER associated with the
subscription;
o the target parameter specifies the PRESENTITY associated with the
presence information;
o the transID parameter specifies the transaction-identifier
associated with this operation; and,
o the presence information for the PRESENTITY.
There is no application response to the notify operation.
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3.4.3 The Unsubscribe Operation
When an application wants to terminate a subscription, it invokes the
unsubscribe operation.
The unsubscribe operations has these parameters:
o the watcher parameter specifies the WATCHER associated with the
subscription;
o the target parameter specifies the PRESENTITY associated with the
presence information; and,
o the transID parameter specifies the transaction-identifier
associated with this operation.
When the service is informed of the unsubscribe operation, it
performs these steps:
1. If the watcher and target parameters do not refer to an in-
progress subscribe operation for the application, a response
operation having status "failure" is invoked.
2. Otherwise, the in-progress subscribe operation for the
application is terminated, and a response operation having status
"success" is invoked by the service.
Note that following a successful unsubscribe operation, the WATCHER
may receive further notifications. Although the service will no
longer invoke the notify operation after successfully processing a
unsubscribe operation, earlier notify operations may still be in
progress.
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4. Security Considerations
This memo makes no specific requirements on security procedures for
interoperation between IM systems. Accordingly, trust between
interconnected IM systems is determined in a bilateral matter.
However this memo does require that each IM system control access to
its Instant Messaging and Presence services. Consult both RFC 2778
and RFC2779 for a discussion of security considerations for for IM
systems.
4.1 Threats
Attacks, of concern for instant messaging, include access, deletion,
insertion, reordering and modification of messages by unauthorized
principals. Replay is a combination of a subset of these attacks.
These attacks can take place in the communication links between
sending client and its server, between two servers, between the
receiving client and its server, or by attacking any of the hosts
involved. This document, not being concerned with client-server
interchanges, only addresses threats aimed at server-server
communication.
Countermeasures against unauthorized access are encrypted
communication and encrypted messages.
Countermeasures against insertion of false messages are
authentication and authorization of sending servers and strongly
signed messages.
Countermeasures against reordered messages are date-stamped or
serial-numbered messages, coupled with digital signatures that
include the date or serial number, if modification is not otherwise
guarded against.
Countermeasures against replayed messages are date stamps and unique
message IDs, coupled with digital signatures that include the date or
serial number, if modification is not otherwise guarded against.
Countermeasures against deletion of messages are integrity-protected
connections between servers where the server's identity is verified.
Serial-numbered messages can also be useful in detecting deleted
messages.
Attacks that target the server hosts rather than the communication
channels can successfully defeat all countermeasures that depend on
host security. Digital signatures and encrypted messages do not
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depend on host security, for intermediate systems, but cannot by
themselves guard against deletion or reordering of messages.
For presence, the attacks include giving presence information to
unauthorized watchers, not reporting watcher information back to a
presentity, and insertion, modification, deletion and replay of
presence update messages. The same set of countermeasures are
relevant.
Instant messaging and presence systems can provide security at two
levels: hop-by-hop and/or end-to-end.
4.2 Hop-by-hop security
A useful but imperfect level of security can be provided on a hop-by-
hop basis, with all aspects of the communication including message
content and originator verification, using transport level security
between servers. The main drawback of this approach is that it
requires that each server that handles message or presence
information must be trusted. But it is relatively easy to deploy,
because it depends only on bilateral arrangements between directly
communicating servers.
The underlying principles for using hop-by-hop security are:
(a) each server and/or domain must keep their own house in order,
ensuring that operations and information accesses are allowed only to
appropriately authorized parties, and
(b) each server and/or domain must make its own choices about the
levels of trust to be established to any other server and/or domain
with which they directly communicate. [[[Some debate about the degree
of trust necessary between servers. /dc]]]
When passing IM and presence information between services using
different protocols, a gateway system MUST be capable of using
security mechanisms appropriate to each of the protocols concerned,
and must have access to keys needed to authenticate any other system
with which it needs to directly communicate in a secure fashion.
[[[SUGGESTION: to allow the use of common keys across different
protocols, we might say that hop-by-hop security should be based on
SASL, and specify specific profiles that should be used. This
doesn't buy anything at the protocol level, but it might make it
easier to leverage some common key-distribution infrastructure, and
avoid having to distribute different keys for communicating with a
gateway using different protocols.]]]
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4.3 End-to-end security
End-to-end security is widely regarded as being more satisfactory
than hop-by-hop security, as the need to trust intermediate parties
is reduced. However, some aspects of end-to-end security are
difficult to achieve because they need bilateral arrangement between
any pair of communicating parties about acceptable security standards
to use, and key exchange. Reliance on bilateral agreements does not
scale well. A moderating alernative is a third-party certification
service and this approach, so far, has not found large-scale use.
The two IETF standards for end-to-end MIME object security are
OpenPGP[7] and S/MIME[8]. They require a public key operation for
each message. For repeated, short transactions, this overhead can be
onerous. A version of these specifications which permited re-use of
the public key across multiple messages would greatly reduce instant
messaging overhead.
4.3.1 Instant messages
End to end security for instant messages can be provided using any of
the MIME-based security mechanisms (S/MIME [8], OpenPGP [7]), as
instant message payload content is not interpreted or reformatted in
transit.
[[[NOTE: may need to say something about allowable MIME C-T-Es?]]]
This specification allows any pair of communicating parties to use
any MIME-based security framework for instant messages (c.f. section
2.3), but mechanisms for establishing the required bilateral
arrangements and key exchange are not specified here.
4.3.2 Presence service
The situation regarding end-to-end security for presence services is
unclear, as there is no common encapsulation framework specified for
presence, and the presence data itself is not invariant across
different IM services.
[[[NOTE: this raises a case for fixing the presence information to a
specific format if end-to-end security capability is to be a
requirement.]]]
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5. IANA Considerations
The IANA assigns the "im" and "pres" URL schemes.
5.1 The IM URI Scheme
The Instant Messaging (IM) URI scheme designates an Internet
resource, namely an INSTANT INBOX.
The syntax of an IM URL has the form:
"im:" addr-spec
where "addr-spec" is defined in RFC 822.
5.2 The PRES URI Scheme
The Presence (PRES) URI scheme designates an Internet resource,
namely a PRESENTITY or WATCHER.
The syntax of a PRES URL has the form:
"pres:" addr-spec
where "addr-spec" is defined in RFC 822.
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6. The Common Service DTD
<!--
DTD for the IM common profile, as of 2000-08-16
Refer to this DTD as:
<!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN"
"http://xml.resource.org/syntaxes/IM/im-common.dtd">
%IMCOMMON;
-->
<!--
DTD data types:
entity syntax/reference example
====== ================ =======
a language tag
LANG c.f., [RFC-1766] "en", "en-US", etc.
seconds
SECONDS 0..2147483647 600
unique-identifier
UNIQID 1..2147483647 42
authoritative identity
URI c.f., [RFC-2396] http://invisible.net/
-->
<!ENTITY % LANG "NMTOKEN">
<!ENTITY % SECONDS "CDATA">
<!ENTITY % UNIQID "CDATA">
<!ENTITY % URI "CDATA">
<!--
Abstract syntax for the response operation
-->
<!ELEMENT response (#PCDATA)>
<!ATTLIST response
status (success | failure | indeterminant) #REQUIRED
transID %UNIQID; #REQUIRED
duration %SECONDS; #IMPLIED
xml:lang %LANG; #IMPLIED
>
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7. The Messaging Service DTD
<!--
DTD for the abstract IM messaging service, as of 2000-08-16
Refer to this DTD as:
<!ENTITY % IMMESSAGING PUBLIC "-//Blocks//DTD IM MESSAGING//EN"
"http://xml.resource.org/syntaxes/IM/im-messaging.dtd">
%IMMESSAGING;
-->
<!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN"
"http://xml.resource.org/syntaxes/IM/im-common.dtd">
%IMCOMMON;
<!--
DTD data types:
entity syntax/reference example
====== ================ =======
INBOX c.f., Section 5.1 im:fred@example.com
-->
<!ENTITY % INBOX "CDATA">
<!--
Abstract syntax for the message operation
-->
<!ELEMENT message (#PCDATA)>
<!ATTLIST message
source %INBOX; #REQUIRED
destination %INBOX; #REQUIRED
transID %UNIQID; #REQUIRED
>
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8. The Presence Service DTD
<!--
DTD for the abstract IM presence service, as of 2000-08-16
Refer to this DTD as:
<!ENTITY % IMPRESENCE PUBLIC "-//Blocks//DTD IM PRESENCE//EN"
"http://xml.resource.org/syntaxes/IM/im-presence.dtd">
%IMPRESENCE;
-->
<!ENTITY % IMCOMMON PUBLIC "-//Blocks//DTD IM COMMON//EN"
"http://xml.resource.org/syntaxes/IM/im-common.dtd">
%IMCOMMON;
<!--
DTD data types:
entity syntax/reference example
====== ================ =======
PRESENTITY c.f., Section 5.2 pres:fred@example.com
-->
<!ENTITY % PRESENTITY "CDATA">
<!--
Abstract syntax for presence information
-->
<!ELEMENT presence (tuple+)>
<!ATTLIST presence
entityInfo %URI; ""
>
<!ELEMENT tuple (#PCDATA)>
<!ATTLIST tuple
destination %URI; #REQUIRED
status (open | closed) #REQUIRED
>
<!--
Abstract syntax for the subscribe operation
-->
<!ELEMENT subscribe EMPTY>
<!ATTLIST subscribe
watcher %PRESENTITY; #REQUIRED
target %PRESENTITY; #REQUIRED
duration %SECONDS; #REQUIRED
transID %UNIQID; #REQUIRED
>
<!--
Abstract syntax for the notify operation
-->
<!ELEMENT notify (presence)>
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<!ATTLIST notify
watcher %PRESENTITY; #REQUIRED
target %PRESENTITY; #REQUIRED
transID %UNIQID; #REQUIRED
>
<!--
Abstract syntax for the unsubscribe operation
-->
<!ELEMENT unsubscribe EMPTY>
<!ATTLIST unsubscribe
watcher %PRESENTITY; #REQUIRED
target %PRESENTITY; #REQUIRED
transID %UNIQID; #REQUIRED
>
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9. The Presence Information DTD
<!--
DTD the IM presence information of 2000-11-6
Refer to this DTD as:
<!ENTITY % IMPRESENCEINFO PUBLIC "-//Blocks//DTD IM PRESENCE//EN"
"http://xml.resource.org/syntaxes/IM/im-presence-info.dtd">
%IMPRESENCEINFO;
-->
<!ENTITY % IMCOMMON PUBLIC
"-//Blocks//DTD IM COMMON//EN"
"http://xml.resource.org/syntaxes/IM/im-common.dtd">
%IMCOMMON;
<!--
DTD data types: entity syntax/reference example
====== ================ =======
PRESENTITY c.f., Section 5.2 pres:Fred@example.com
-->
<!ENTITY % PRESENTITY "CDATA">
<!--
Abstract syntax for presence information -->
<!ELEMENT presence (tuple+)>
<!ATTLIST presence
entityInfo %URI; ""
>
<!ELEMENT tuple (#PCDATA)>
<!ATTLIST tuple
destination %URI; #REQUIRED
status (open | closed) #REQUIRED
>
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References
[1] Crocker, D., "Standard for the format of ARPA Internet text
messages", RFC 822, STD 11, Aug 1982.
[2] Mockapetris, P.V., "Domain names - concepts and facilities",
RFC 1034, STD 13, Nov 1987.
[3] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[4] Callas, J., Donnerhacke, L., Finney, H. and R. Thayer, "OpenPGP
Message Format", RFC 2440, November 1998.
[5] Klyne, G., "XML coding of RFC822 messages", I-D draft-klyne-
message-rfc822-xml-00.txt, November 2000.
[6] Ramsdell, B., "S/MIME Version 3 Certificate Handling", RFC
2632, June 1999.
[7] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[8] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[9] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[10] Allocchio, C., "GSTN Address Element Extensions in E-mail
Services", RFC 2846, June 2000.
Authors' Addresses
Dave Crocker
Brandenburg Consulting
675 Spruce Drive
Sunnyvale, CA 94086
US
Phone: +1 408 246 8253
EMail: dcrocker@dcrocker.net
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Athanassios Diacakis
Network Projects Inc.
4516 Henry Street
Suite 113
Pittsburgh, PA 15213
US
Phone: +1 412 681 6950 x202
EMail: thanos@networkprojects.com
Florencio Mazzoldi
Network Projects Inc.
4516 Henry Street
Suite 113
Pittsburgh, PA 15213
US
Phone: +1 412 681 6950
EMail: flo@networkprojects.com
Christian Huitema
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
US
EMail: huitema@microsoft.com
Graham Klyne
Content Technologies
Henley Business Centre, Newtown Road
Oxfordshire RG9 1HG
UK
Phone: +44 118 930-1300
EMail: GK@Dial.pipex.com
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Marshall Rose
Invisible Worlds
1179 North McDowell Boulevard
Petaluma 94954-655
US
Phone: +1 916-483-8878
EMail: mrose@dbc.mtview.ca.us
Jonathan Rosenberg
dynamicsoft
200 Executive Drive
Suite 120
West Orange, NJ 07052
US
EMail: jdrosen@dynamicsoft.com
Robert Sparks
dynamicsoft
200 Executive Drive
Suite 120
West Orange, NJ 07052
US
EMail: rsparks@dynamicsoft.com
Hiroyasu Sugano
Fujitsu Laboratories Ltd.
64 Nishiwaki, Ohkubo-cho
Akashi 674-8555
JP
EMail: suga@flab.fujitsu.co.jp
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Appendix A. IM URL IANA Registration Template
This section provides the information to register the im: instant
messaging URL.
A.1 URL scheme name
im
A.2 URL scheme syntax
The syntax replicates the existing mailto: URL syntax specified in
RFC2368. The ABNF is:
IM-URL = "im:" [ to ] [ headers ]
to = #mailbox
headers = "?" header *( "&" header )
header = hname "=" hvalue
hname = *urlc
hvalue = *urlc
A.3 Character encoding considerations
Representation of non-ASCII character sets in local-part strings is
limited to the standard methods provided as extensions to RFC 822[1]
A.4 Intended usage
Use of the im: URL follows closely usage of the mailto: URL. That is,
invocation of an IM URL will cause the user's instant messaging
application to start, with destination address and message headers
fill-in according to the information supplied in the URL.
A.5 Applications and/or protocols which use this URL scheme name
It is anticipated that protocols compliant with RFC2779, and meeting
the interoperability requirements specified here, will make use of
this URL scheme name.
A.6 Interoperability considerations
The underlying exchange protocol used to send an instant message may
vary from service to service. Therefore complete, Internet-scale
interoperability cannot be guaranteed. However, a service conforming
to this specification permits gateways to achieve interoperability
sufficient to the requirements of RFC2779.
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A.7 Security considerations
When IM URLs are placed in instant messaging protocols, they convey
the identity of the sender and/or the recipient. In some cases,
anonymous messaging may be desired. Such a capability is beyond the
scope of this specification.
A.8 Relevant publications
RFC2779, RFC2778
A.9 Person & email address to contact for further information
Dave Crocker<dcrocker@dcrocker.net>
A.10 Author/Change controller
This scheme is registered under the IETF tree. As such, IETF
maintains change control.
A.11 Applications and/or protocols which use this URL scheme name
Instant messaging service; presence service
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Appendix B. PRES URL IANA Registration Template
This section provides the information to register the pres: presence
URL .
B.1 URL scheme name
pres
B.2 URL scheme syntax
The syntax replicates the existing mailto: URL syntax specified in
RFC2368. The ABNF is:
PRES-URL = "pres:" [ to ] [ headers ]
to = #mailbox
headers = "?" header *( "&" header )
header = hname "=" hvalue
hname = *urlc
hvalue = *urlc
B.3 Character encoding considerations
Representation of non-ASCII character sets in local-part strings is
limited to the standard methods provided as extensions to RFC 822[1]
B.4 Intended usage
Use of the pres: URL follows closely usage of the mailto: URL. That
is, invocation of an PRES URL will cause the user's instant messaging
application to start, with destination address and message headers
fill-in according to the information supplied in the URL.
B.5 Applications and/or protocols which use this URL scheme name
It is anticipated that protocols compliant with RFC2779, and meeting
the interoperability requirements specified here, will make use of
this URL scheme name.
B.6 Interoperability considerations
The underlying exchange protocol used for presence may vary from
service to service. Therefore complete, Internet-scale
interoperability cannot be guaranteed. However, a service conforming
to this specification permits gateways to achieve interoperability
sufficient to the requirements of RFC2779.
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B.7 Security considerations
When PRES URLs are placed in presence protocols, they convey the
identity of the sender and/or the recipient. In some cases, anonymous
messaging may be desired. Such a capability is beyond the scope of
this specification.
B.8 Relevant publications
RFC2779, RFC2778
B.9 Person & email address to contact for further information
Dave Crocker<dcrocker@dcrocker.net>
B.10 Author/Change controller
This scheme is registered under the IETF tree. As such, IETF
maintains change control.
B.11 Applications and/or protocols which use this URL scheme name
Instant messaging service; presence service
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Appendix C. Issues of Interest
This appendix briefly discusses issues that may be of interest when
designing an interoperation gateway.
C.1 Address Mapping
When mapping the service described in this memo, mappings which place
special information into the im: address local-part MUST use the
meta-syntax defined in RFC 2486[10].
C.1.1 Source-Route Mapping
The easiest mapping technique is a form of source-routing and usually
is the least friendly to humans having to type the string. Source-
routing also has a history of operational problems.
Use of source-routing for exchanges between different services is by
a transformation that places the entire, original address string
into the im: address local part and names the gateway in the domain
part.
For example, if the destination INSTANT INBOX is
"pepp://example.com/fred", then, after performing the necessary
character conversions, the resulting mapping is:
im:pepp=example.com/fred@relay-domain
where "relay-domain" is derived from local configuration information.
Experience shows that it is vastly preferrable to hide this mapping
from end-users Ãù if possible, the mapping should be performed
automatically by the underlying software.
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Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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included on all such copies and derivative works. However, this
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the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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